Vehicles include a fuel vapor canister to trap diurnal, running loss, and refueling recovery fuel vapors. Such fuel vapor canisters trap the fuel vapors with an adsorbent media, such as activated carbon, and purge the stored fuel vapors to the engine for combustion. However, in hybrid vehicles that are propelled at least periodically by an electric motor and not the engine, the engine may not run for a relatively long duration, particularly after a refueling event has occurred. Because any adsorbed fuel vapors are stored in the canister until the engine can consume them, the long durations between engine operations can lead to high vapor load on the canister, causing bleed-through emissions and other issues. Further, because engine heat is not available during electric operation, the fuel vapor canister may drop in temperature, reducing the efficiency of a subsequent fuel vapor purge.
The inventors herein have recognized the above issues and offer an approach to at least partly address them. In one embodiment, a method comprises, during a purge of a fuel vapor canister, adjusting a heater of the fuel vapor canister based on a rate of a purge flow exiting the fuel vapor canister and a concentration of hydrocarbons released from the fuel vapor canister.
In this way, the one or more heaters of the fuel vapor canister may be adjusted based on characteristics of the endothermic reaction occurring during the purge in order to maintain the canister at a temperature that promotes efficient release of the fuel vapors from the canister without wasting excess energy to operate the heaters during the entire purge process. For example, activation of the one or more heaters may be delayed following start of purge until the endothermic reaction, as measured by the concentration of fuel vapors being released from the fuel vapor canister, reaches a high enough rate to significantly affect canister temperature and thus hinder subsequent release of the fuel vapors. Once the concentration of fuel vapors reaches a threshold level, the one or more heaters may be activated to promote additional fuel vapor release from the storage media.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.